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SpringBoot源码学习系列之启动原理简介

smileNicky 人气:4

本博客通过debug方式简单跟一下Springboot application启动的源码,Springboot的启动源码是比较复杂的,本博客只是简单梳理一下源码,浅析其原理

为了方便跟源码,先找个Application类,打个断点,进行调试,如图所示:

step into,run方法调用了SpringApplication的run方法

通过debug,Springboot启动过程,会先执行如下关键的构造函数

分析构造函数源码:

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
        this.resourceLoader = resourceLoader;
        Assert.notNull(primarySources, "PrimarySources must not be null");
        this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
        // 判断当前的web类型
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        //设置初始化的ApplicationInitializer类,从类路径下面的META-INF/spring.factories配置文件获取所有的ApplicationInitializer保存起来
        setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
        //同理,从类路径下面的META-INF/spring.factories配置文件获取所有的ApplicationListener保存起来
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        //从多个配置类中找到有main方法的主配置类
        this.mainApplicationClass = deduceMainApplicationClass();
    }

注意:上面过程其实就是创建Springboot的Application启动类的过程

deduceFromClasspath方法是判断web类型的

继续debug ApplicationContextInitializer这些Initializer类,可以说是初始化类的设置过程

SpringFactoriesLoader.loadFactoryNames(type, classLoader)获取所有的Initializer类的类名

Evaluate可以看出扫描到如下的类

继续debug,这个是Spring框架的底层类

找到主要的源码,loadSpringFactories方法也是从如下的位置获取配置信息的

从META-INF/spring.factories获取对应的配置信息

框架的文件位置在autoconfiguration工程里,显然如果要自定义Initializer类的话,自己新建一些Initializer类,然后自己写个META-INF/spring.factories类,也是可以被扫描到的

private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
        //用一个ConcurrentReferenceHashMap来缓存信息
        MultiValueMap<String, String> result = cache.get(classLoader);
        if (result != null) { //缓存读取到配置信息,返回缓存数据
            return result;
        }
        // 缓存读取不到的情况,重新从META-INF/spring.factories配置文件读取
        try {
            Enumeration<URL> urls = (classLoader != null ?
                    classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
                    ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
            result = new LinkedMultiValueMap<>();
            // 遍历循环读取配置信息
            while (urls.hasMoreElements()) {
                URL url = urls.nextElement();
                UrlResource resource = new UrlResource(url);
                // 用PropertiesLoaderUtils工具类读取资源文件
                Properties properties = PropertiesLoaderUtils.loadProperties(resource);
                for (Map.Entry<?, ?> entry : properties.entrySet()) {
                //获取到Initializer对应的全类名
                    String factoryTypeName = ((String) entry.getKey()).trim();
                    for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
                        result.add(factoryTypeName, factoryImplementationName.trim());
                    }
                }
            }
            // 重新放在缓存里
            cache.put(classLoader, result);
            return result;
        }
        catch (IOException ex) {
            throw new IllegalArgumentException("Unable to load factories from location [" +
                    FACTORIES_RESOURCE_LOCATION + "]", ex);
        }
    }

ApplicationInitializer类的全类名都被扫描到之后,返回刚才的源码,继续看看,如图,从命名看应该是进行类的实例化过程

step into,果然是的,还是调用了Spring框架的底层工具类,BeanUtils进行类的实例化过程

setListeners方法的过程同理,本文就不详细分析:

继续往下debug,deduceMainApplicationClass方法

private Class<?> deduceMainApplicationClass() {
        try {
            //获取运行时的堆栈属性数组
            StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
            for (StackTraceElement stackTraceElement : stackTrace) {
                //有main方法的Application类返回
                if ("main".equals(stackTraceElement.getMethodName())) {
                    return Class.forName(stackTraceElement.getClassName());
                }
            }
        }
        catch (ClassNotFoundException ex) {
            // Swallow and continue
        }
        return null;
    }

获取到的就是创建Springboot工程时的Application类

Springboot的Application类创建成功之后,才真正开始执行run方法

public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
        //校验java.awt.headless的
        configureHeadlessProperty();
        //从META-INF/spring.factories获取SpringApplicationRunListeners,和前面的分析同理,本文就不详细介绍
        SpringApplicationRunListeners listeners = getRunListeners(args);
        //回调SpringApplicationRunListeners 的starting方法
        listeners.starting();
        try {
            //封装命令行参数
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            //准备环境,环境创建完成之后,再回调SpringApplicationRunListeners 的environmentPrepared方法,表示环境准备好
            ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
            configureIgnoreBeanInfo(environment);
            //控制台打印Banner信息的,后面再简单分析
            Banner printedBanner = printBanner(environment);
            // 创建Spring的IOC容器,创建过程比较复杂,会分析是web类型的ioc容器,还是普通的ioc容器等等
            context = createApplicationContext();
            exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
                    new Class[] { ConfigurableApplicationContext.class }, context);
            //将environment保存到ioc,执行applyInitializers方法,applyInitializers方法执行完成之后,再回调SpringApplicationRunListeners的contextPrepared方法
            //applyInitializers方法作用:回调之前保存的所有的ApplicationContextInitializer的initialize方法
            prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            //刷新ioc容器,其实就是ioc容器的初始化过程,还没进行属性设置,后置处理器,仅仅是扫描、创建、加载所有组件等等过程
            refreshContext(context);
            afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
            }
            //回调所有SpringApplicationRunListener的started方法
            listeners.started(context);
            //从ioc容器中获取所有的ApplicationRunner和CommandLineRunner进行回调,ApplicationRunner先回调,CommandLineRunner再回调
            callRunners(context, applicationArguments);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, exceptionReporters, listeners);
            throw new IllegalStateException(ex);
        }

        try {
            //回调所有SpringApplicationRunListener的running方法
            listeners.running(context);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, exceptionReporters, null);
            throw new IllegalStateException(ex);
        }
        //Springboot应用启动成功后,才返回启动的ioc容器
        return context;
    }

回顾一下前面源码的环境准备方法,找重点代码,如图,可以看出环境准备完成后会回调SpringApplicationRunListener的environmentPrepared方法,表示环境准备完成

banner打印的方法,如图,执行完成,控制台的banner信息就打印出来了:

ioc初始化之前,会执行applyInitializers方法,执行完成后,再回调SpringApplicationRunListener的contextPrepared方法

applyInitializers():回调之前保存的所有的ApplicationContextInitializer的initialize方法

从ioc容器中获取所有的ApplicationRunner和CommandLineRunner进行回调

ok,从源码的简单分析,可以看出有几个重要的事件监听机制,下面引用尚硅谷视频的例子:

只需要放在ioc容器中的有:

  • ApplicationRunner
@Component
public class HelloApplicationRunner implements ApplicationRunner {
    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("ApplicationRunner...run....");
    }
}
  • CommandLineRunner
@Component
public class HelloCommandLineRunner implements CommandLineRunner {
    @Override
    public void run(String... args) throws Exception {
        System.out.println("CommandLineRunner...run..."+ Arrays.asList(args));
    }
}

配置在META-INF/spring.factories的有:

  • ApplicationContextInitializer
public class HelloApplicationContextInitializer implements
ApplicationContextInitializer<ConfigurableApplicationContext> {
    @Override
    public void initialize(ConfigurableApplicationContext applicationContext) {
      
 System.out.println("ApplicationContextInitializer...initialize..."+applicationContext);
    }
}
  • SpringApplicationRunListener
package com.example.springboot.web.listener;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.SpringApplicationRunListener;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.env.ConfigurableEnvironment;

public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {

    //必须有的构造器
    public HelloSpringApplicationRunListener(SpringApplication application, String[] args){

    }

    @Override
    public void starting() {
        System.out.println("SpringApplicationRunListener...starting...");
    }

    @Override
    public void environmentPrepared(ConfigurableEnvironment environment) {
        Object o = environment.getSystemProperties().get("os.name");
        System.out.println("SpringApplicationRunListener...environmentPrepared.."+o);
    }

    @Override
    public void contextPrepared(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener...contextPrepared...");
    }

    @Override
    public void contextLoaded(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener...contextLoaded...");
    }


}

配置(META-INF/spring.factories)

org.springframework.context.ApplicationContextInitializer=\
com.example.springboot.web.listener.HelloApplicationContextInitializer

org.springframework.boot.SpringApplicationRunListener=\
com.example.springboot.web.listener.HelloSpringApplicationRunListener

例子下载:github下载链接

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